The usual brushes of this type generally comprise relatively long bristles disposed in a spiral layer around a core formed by a twisted iron wire. The number of bristles of the brush is measured by the number of bristles forming one turn of the spiral layer having an angular aperture equal to 360.degree..
Relatively flexible bristles were used in the prior art so as to give the brush the general property of appropriate flexibility. Given that the brush was to be used to make up a support as delicate as the eyelashes, the maximum diameter of the bristles was generally approximately 0.08 mm. The bristles used were generally made of polyamide. In this case, given that the bristles of small diameter referred to hereinabove have in themselves very low rigidity, it was ensured that a sufficient quantity of mascara was taken up and that the eyelashes were brushed correctly at the time of application by always using more than 50 bristles per turn so that the spiral layer was sufficiently thick to obtain the desired result. The spiral layer of bristles generally had a pitch of approximately 2 mm and the bristles were substantially parallel in the thickness of the layer.
However, it became clear that brushes of this kind did not ensure good distribution of the make-up product over the eyelashes upon use, as, in practice, the mascara is often placed over the eyelashes in blobs with no homogeneity, so that the user has to effect repeated brushing operations until an approximately uniform coating of the eyelashes is obtained. This disadvantage results firstly from the fact that these brushes comprise a large number of bristles packed closely together in the spiral layer, so that, at the time of application, the eyelashes, the diameter of which is generally between 0.08 and 0.12 mm, cannot traverse the layer of bristles and can only move into the gaps between the successive turns of the spiral layer of bristles. The eyelashes therefore cannot be separated from one another at the time of application, as would be desirable. However, the said disadvantage results moreover secondly from the fact that when a brush of this kind of the prior art takes up the mascara, the latter is distributed poorly over the brush, as a mascara applicator generally comprises a mascara container and a removable cap which is adapted to close the container and which forms a handle for the manipulation of a make-up brush carried by the end of a stem integral with the said cap. In the closed position of the container, the stem and the brush associated therewith penetrate into the container. When the stem is removed from the container, a certain quantity of mascara is taken up on the brush and this can then be applied to the eyelashes. The brush penetrates into the interior of the container via a substantially circular orifice surrounded by a flexible lip, the function of which is to exert a wiping action on the bristles of the brush in order to eliminate excess make-up product taken up on the brush inside the container. The diameter of this circular orifice is smaller than the diameter of the brush measured at the tip of the bristles, so that the flexible lip which surrounds the orifice can exert its wiping action when the brush is removed from the container. As the bristles of the brush are relatively flexible and are disposed with a relatively high density in the spiral layer of bristles, they bend over in the direction of the core when the layer passes through the wiper lip and, by virtue of this deformation, they cause the bristles of the adjacent turn to "bend over", resulting in the fact that the make-up product tends to accumulate in the region of the brush situated just around the core. Under these conditions, at the time of application, the user will have difficulty obtaining a completely uniform and homogeneous coating of the eyelashes by the make-up product in one single passage of the brush, the make-up product gradually migrating towards the ends of the bristles initially not heavily loaded with product. Migration of this kind is moreover effected in a random manner. This results in heterogeneous and generally light make up.
An improved make-up brush obviating the aforesaid disadvantages was already proposed in French Patent No. 2 607 373. It was proposed to use bristles of a larger diameter and to ensure that these bristles had a greater spacing from one another by using a small number of bristles per turn. The brush proposed in this manner thus consists of more thinned out and harder bristles. It is harder to the touch, but nevertheless does not give the impression of hardness during making up. The reduction in the number of bristles per turn means that it is possible for the bristles of the spiral layer situated substantially in one single radial plane of the brush to adopt at random, starting from the zone in which they are gripped between the turns, an angular spacing from the iron wire which forms the core relative to the mean spiral surface of the spiral layer of bristles. In other words, the edge of the spiral layer of bristles becomes all the wider the more the number of bristles per turn is reduced. It has been noted that it was possible in this manner to obtain brushes the spiral layer of which became virtually invisible, the bristles of one turn of the spiral layer being able to come into the vicinity of the bristles of the adjacent turn of the same spiral layer as a result of the random angular spacing adopted by the bristles in their gripped zone. This particular result is obtained when the bristles have a diameter of between 0.10 and 0.25 mm and when the number of bristles per turn is between 10 and 40. It has been noted that these improved brushes improve the uniformity of the loading with make-up product of the bristles of the brush from their base to their tip and moreover improve the combing of the eyelashes during making up, as a result, on the one hand, of the greater firmness of the bristles, the diameter of which was increased and, on the other hand, of their spacing as a result of the disappearance of the spiral effect.
According to this invention, it was acknowledged that it was not possible to reduce the number of bristles of the brush to below 10 bristles per turn as a result of the fact that the "hedgehog" formed by a brush of this kind would not have been sufficient to allow for satisfactory making up, as the eyelashes could then traverse the brush virtually without touching a bristle loaded with product. This lower limit for the number of bristles of a brush was moreover generally acknowledged as a result of the fact that the person skilled in that art felt that the reduction in the number of bristles of a brush of the type defined hereinabove would always lead to the disappearance of the spiral effect and the emergence of a "hedgehog" type brush as a result of random angular spacing of the bristles relative to the mean spiral surface of the layer of bristles. It became clear, moreover, that this effect increased as the number of bristles per turn was reduced for a given bristle diameter.